1. Field of the Invention
The present invention relates to a treatment apparatus for performing a predetermined treatment for a workpiece such as a semiconductor wafer.
2. Description of the Related Art
In semiconductor fabrication processes, various treatment apparatuses that form an oxide film on a semiconductor wafer, which is a workpiece, form a thin film on a semiconductor wafer corresponding to heat CVD method, and form impurity regions with different concentrations on a semiconductor wafer corresponding to heat diffusion method have been used. In the following description, the semiconductor wafer may be referred to as simply a wafer.
In recent years, upright type heat treatment apparatuses have been widely used instead of conventional flat type heat treatment apparatuses. As an example of the upright type heat treatment apparatuses, a wafer boat (which serves as a holding member) that contains a large number of wafers is loaded into a nearly-cylindrical upright type treatment chamber (process tube). The inside of the process tube is heated in an atmosphere of a predetermined treatment gas so as to perform various treatments for the wafers.
In the conventional heat treatment apparatus of this type, a manifold is disposed below the process tube (that is made of quartz or the like). An exhaust pipe and a delivery pipe are disposed on the manifold so as to exhaust waste gas therefrom and to deliver clean gas thereto. A heater is disposed around the process tube so as to heat the inside thereof at a desired temperature.
The wafer boat, which contains a large number of wafers, is transferred from a loading chamber to the process tube by a boat elevator that constructs a transfer mechanism. At this point, a flange of the wafer boat is brought into contact with the manifold so as to airtightly close the inside of the process tube.
An input/output means is disposed in a transfer chamber adjacent to the loading chamber. The input/output means inputs and outputs the wafers accommodated in a wafer carrier to and from the wafer boat.
When the wafers are treated by the heat treatment apparatus, they are contained in the wafer boat in an atmosphere of an inert gas (such as nitrogen N.sub.2), namely an atmosphere of non-oxygen. The wafer boat is raised and loaded into the process tube by the boat elevator. Thereafter, the N.sub.2 gas is exhausted through the exhaust pipe. When the inside of the process tube becomes a vacuum of a predetermined level, a treatment gas is delivered into the process tube through the delivery pipe so as to perform a desired treatment. In the above-described conventional apparatus, a load lock chamber construction where the inside of the loading chamber is airtightly closed and air and gas are exhausted therefrom has been used. As another construction of the apparatuses, the inside of the loading chamber is always kept at the pressure of an atmosphere of clean air.
In the above-described upright type heat treatment apparatuses, when the wafer carrier is input and output to and from the transfer chamber, which accommodates the wafer carrier, a door disposed on the transfer chamber is opened and closed, respectively. The wafer carrier is transferred to the vacuum chamber by an automatic guided vehicle (AGV) or the operator in the condition that the wafers contained in the wafer carrier are exposed to clean air. In addition, the wafers that have been treated are output from the vacuum chamber in the condition that the wafers are exposed to the clean air.
Thus, the outside of the transfer chamber (namely the entire clean room in which the operator and the like work) should be kept at a cleanliness level equal to or close to the cleanliness level of the transfer chamber and the loading room (for example, class 1) so as to prevent particles from adhering to the wafers.
When the clean room is constructed, the construction cost of the clean room is proportional to the cleanliness level thereof. Thus, if the working regions for the wafer carrier, the operator, and the like were constructed with such a high cleanliness level, the construction cost would remarkably increase.
In addition, since the large clean room should be kept with the high cleanliness level, the running cost thereof will also increase.